Motor driven valve and cooling/heating system

ABSTRACT

To provide a motor-driven valve without requirement that a check valve is separately connected through piping in parallel and without a built-in check valve. A motor-driven valve  1  according to the present invention having a valve body  7  linearly moving by rotation of a rotor  15  of an electric motor and controlling a valve opening between the valve body  7  and a valve seat  6 , and the motor-driven valve  1  is characterized in that: in a first valve opening range, the valve opening and flow rate of fluid have a predetermined correlation, and in a second valve opening range, flow rate more or equal to four time as much as controllable maximum flow rate in the first valve opening range can pass the valve  1 . It is possible to use the motor-driven valve  1  for cooling/heating systems and to control flow rate of refrigerant in cooling in the first valve opening range and allow a large amount of the refrigerant to pass the valve in heating, so that only one electronic valve can satisfy performance of conventional valves.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Japanese Patent ApplicationNo. 2007-174783 entitled MOTOR-DRIVEN VALVE AND COOLING/HEATING SYSTEMfiled on Jul. 3, 2007.

STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT

Not Applicable.

BACKGROUND

1. Field of the Invention

The present invention relates to a motor-driven valve that can be usedas an electronic expansion valve with check valve function incooling/heating systems and a cooling/heating system with themotor-driven valve.

2. Description of the Related Art

As a conventional cooling/heating system (heat pump cycle), a systemshown in FIG. is used. The cooling/heating system 51 is composed of acompressor 52; a switching valve 53 for switching flow passages forrefrigerant to switch cooling/heating operation; an outdoor heatexchanger 54; a distributor 55 and a thermal expansion valve 56 throughwhich the refrigerant passes in heating; a check valve 57 through whichthe refrigerant passes in cooling; a thermal expansion valve 58 with acheck valve through which the refrigerant passes in cooling/heatingoperations; and an indoor heat exchanger 59, and the refrigerant flowsin a direction of solid-line arrows in cooling, and flows in a directionof broken-line arrows in heating.

In the cooling/heating system 51, in cooling operation, refrigerant gascompressed by the compressor 52 flows into the outdoor heat exchanger 54via the switching valve 53 and is condensed through heat exchange withatmospheric air; the refrigerant flows into the thermal expansion valve58 with a check valve via the check valve 57 to perform insulationexpansion; and then the refrigerant evaporates in the indoor heatexchanger 59 through heat exchange with indoor air to cool the room.

On the other hand, in heating operation, refrigerant gas compressed bythe compressor 52 flows into the indoor heat exchanger 59 via theswitching valve 53 and is condensed through heat exchange with indoorair to warm the room; the refrigerant flows into the thermal expansionvalve 56 via the thermal expansion valve 58 with a check valve so as tobe reduced in pressure; and then the refrigerant evaporates in theoutdoor heat exchanger 54 after passing the distributor 55 and returnsto the compressor 52.

The thermal expansion valve 58 with a check valve used for thecooling/heating system 51 has a built-in check valve, and in an originalflow (in cooling), the valve 58 controls flow rate by an expansion valveportion, and in a reverse flow (in heating), the refrigerant passesthrough the check valve portion. Here, the flow rate of the refrigerantin the check valve portion is remarkably high in comparison to that inthe original flow, so that it is necessary to manage the same flow rateas in connected pipes with almost no pressure loss.

Meanwhile, in order to control flow rate of refrigerant or the like inrefrigeration cycle systems, a conventional motor-driven valve 70 shownin FIG. 6 is used. The motor-driven valve 70 is composed of a valve mainbody 75 having a first flow passage 72 and a second flow passage 73 thatcommunicate with a valve chamber 71; a valve body 77 that contacts withand is separated from a valve seat 76 of the valve main body 75; acylindrical shield case 79; a stator coil 80 disposed outside of thesealed case 79; a rotor 84 that rotates in the sealed case 79 throughmagnetization by feeding current to the stator coil 80 so as to bemovable in a valve opening/closing directions; a male screw pipe 81 anda valve shaft holder 82 that allow the valve body 77 to contact with andbe separated from the valve seat 76 via a valve shaft 74 throughscrew-feeding action with the valve shaft holder 82 by the rotation ofthe rotor 84 and so on. The rotor 84 is composed of a permanent magnet83 and the valve shaft holder 82 fixed to the permanent magnet 83through a stop ring 86.

The motor-driven valve 70 with the above-mentioned construction allowsthe rotor 84 to rotate through magnetization by feeding current to thestator coil 80 and allows the valve shaft holder 82 to rotate also toopen and close the valve. The rotating motion of the valve shaft holder82 is converted to vertical motion of the valve shaft 74, and when thevalve shaft 74 moves downward and the valve body 77 abuts the valve seat76 the flow passages are closed, on the other hand, when the valve shaft74 moves upward and the valve body 77 is separated from the valve seat76 the flow passages are opened.

In the conventional cooling/heating system shown in FIG. 5, although athermal expansion valve with a built-in check valve or a thermalexpansion valve and a check that are connected through a pipe inparallel are used, the check valve portion is large in diameter incomparison to the diameter of an opening of the expansion valve toreduce pressure loss, so that the construction of the thermal expansionvalve with a built-in check valve itself becomes intricate and the sizeof the valve becomes large, resulting in increased manufacturing cost ofthe valve. On the other hand, the construction in which a thermalexpansion valve and a check valve are connected in parallel requiresadditional piping and boding works, resulting in increased area to mountthe valves and increased cost. And, in order to improve save-energyefficiency, an electronic expansion valve is used in place of thethermal expansion valve, which causes almost the same problem asdescribed above.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the aboveproblems in the conventional cooling/heating systems, and the objectthereof is to provide a motor-driven valve that provides the sameperformance as the conventional valve without requirement that a checkvalve is separately connected through piping in parallel and without abuilt-in check valve, and a cooling/heating system with the motor-drivenvalve.

To achieve the above object, the present invention relates to amotor-driven valve having a valve body linearly moving by rotation of arotor of an electric motor and controlling a valve opening between thevalve body and a valve seat, and the motor-driven valve is characterizedin that: in a first valve opening range, the valve opening and flow rateof fluid have a predetermined correlation, and in a second valve openingrange, flow rate more than four time as much as a controllable maximumflow rate in the first valve opening range can pass the valve.

With the motor-driven valve according to the present invention, sinceflow rate of fluid can be controlled in the first valve opening range,and a large amount of fluid can be flown in the second valve openingrange, it is possible, for instance, to use the motor-driven valve forcooling/heating systems and to control flow rate of a refrigerant incooling in the first valve opening range and allow a large amount of therefrigerant to pass the valve in heating. With this, it is avoidable toseparately connect a check valve in parallel to a pipe as well as aproblem caused by using a valve with a built-in check valve, whichincreases cost and size due to intricate construction of the valveitself, can be eliminated, because only one valve can satisfy theperformance of the conventional valve, resulting in decreased cost andsize.

In the above motor-driven valve, driving pulses can be fed to a drivingcoil of the electric motor to control the valve opening, and ratio of anopening area of the valve seat when whole pulses are applied to the areawhen intermediate pulses are applied may be four or more.

Further, in the above motor-driven valve, it is possible that drivingpulses are fed to a driving coil of the electric motor to control thevalve opening; an opening area of the valve seat is three times or morethan a theoretical opening area of the valve seat that is required tocontrol flow rate of the fluid in the first valve opening range; thefluid flow rate in the first valve opening range is controlled withdriving pulses of which width is in a range between more or equal to aquarter and less or equal to two-thirds of whole pulses; and the valveopening is controlled to be maximum with driving pulses when wholepulses are applied.

In addition, in the above motor-driven valve, at the maximum valveopening fluid may flow in an opposite direction to that of fluid flowingin the first valve opening range, which allows, as described above, theflow of the refrigerant in cooling/heating operation to be switched.

Still further, in the above motor-driven valve, ratio of the opening areof the valve seat of the motor-driven valve to a minimum innercross-sectional area of pipes in a system with the motor-driven valvemay be 0.2 or more. With this, pressure loss in a system with themotor-driven valve of the present invention may be suppressed low.

In the above motor-driven valve, a driving screw for converting therotational motion of the rotor to the liner motion of the valve body canbe mounted, and ratio of nominal diameter of the driving screw to adiameter of the valve seat opening may be 1.3 or less. Reducing nominaldiameter of the driving screw makes it possible to reduce frictionalforce generated at a complete screw portion, which causes effect ofincreased load (product of deferential pressure between two flowpassages of fluid across the valve seat and opening area of the valveseat) due to enlarged valve opening area of the valve seat in comparisonto conventional valves to be suppressed small.

In the above motor-driven valve, a spring can be disposed between thevalve body and the rotor, for urging the valve body to the valve seatside, and ratio of compression load to the spring in a fully-closedstate of the valve to product of deferential pressure between two flowpassages across the valve seat in the fully-closed state of the valveand the opening area of the valve seat may be a half or less. With this,it is possible to reduce friction loss at the driving screw portion andthe like at the rotation of the rotor.

In the above motor-driven valve, ratio of a length of a complete screwportion of the driving screw to the nominal diameter of the drivingscrew may be 0.75 or more. Making the nominal diameter of the drivingscrew as small as possible allows, as described above, friction forcegenerated at the complete screw portion to become small, which suppressthe influence in load due to increased opening area of the valve seatsmall.

Further, it is possible to construct the motor-driven valve describedabove such that a tip portion of the valve body is formed to be acircular-truncated-cone shape with reduced diameter toward the tip side;fluid flow rate is controlled by a portion between a side face of thecircular-truncated-cone portion and an inner circumferential face of thevalve seat opening; an angle between the side face of thecircular-truncated-cone portion and an axis of the valve body is 15degree or less; and ratio of a length of the side face in a direction ofthe axis to moving amount of the valve body over whole pulse width is0.7 or less.

In addition, in the motor-driven valve, the diameter of the valve seatopening may be more or equal to 3 mm.

Further, the present invention relates to a cooling/heating system, andthe system is characterized to have a motor-driven valve having a valvebody linearly moving by rotation of a rotor and controlling a valveopening between the valve body and a valve seat, and the motor-drivenvalve is characterized in that: in a first valve opening range, flowrate in cooling operation is controlled, and in a second valve openingrange, in heating operation, refrigerant more than four time as much asa controllable maximum flow rate of refrigerant in the cooling operationcan pass the valve. With the present invention, as described above, itis avoidable to separately connect a check valve in parallel to a pipeas well as a problem caused by using a valve with a built-in checkvalve, which is increased cost and size due to intricate construction ofthe valve itself, can be eliminated, because only one valve can satisfythe performance of the conventional valve, resulting in decreased costand size.

As described above, with the present invention, it becomes unnecessaryto separately connect a check valve to a pipe in parallel and to preparea built-in check valve structure, and the performance of theconventional valve can be satisfied with a single valve with reducedcost and downsizing.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more apparent from the ensuringdescription with reference to the drawings, wherein:

Figure is a cross-sectional view of a motor-driven valve according to anembodiment of the present invention;

FIG. 2 is a graph showing flow rate performance of the motor-drivenvalve shown in FIG. 1;

FIGS. 3A and 3B cross-sectional views showing examples that themotor-driven valve shown in FIG. 1 is used in cooling/heating systems incooling operation and in heating operation respectively;

FIG. 4 is a front view showing a valve body and its neighboring elementsof the motor-driven valve shown in FIG. 1;

FIG. 5 is a flowchart showing a conventional cooling/heating system; and

FIG. 6 is a cross-sectional view of a conventional motor-driven valve.

BEST MODE TO CARRY OUT THE INVENTION

Next, embodiments of the present invention will be explained withreference to drawings.

FIG. 1 shows a motor-driven valve according to an embodiment of thepresent invention. The motor-driven valve 1 roughly comprises: a valvemain body 5 having a first flow passage 3 and a second flow passage 4that communicate with a valve chamber 2; a valve body 7 that contactswith and is separated from a valve seat 6 of the valve main body 5; acylindrical shield case 9; a stator coil (driving coil) 10 disposedoutside of the sealed case 9; a rotor 15 that rotates in the sealed case9 through magnetization by feeding current to the stator coil 10 so asto be movable in a valve opening/closing directions and is provided witha permanent magnet 14 fixed to a cylindrical valve shaft holder 12through a stop ring 13 and the like; a male screw pipe 11 and the valveshaft holder 12 that allow the valve body 7 to contact with and beseparated from the valve seat 6 through screw-feeding action by therotation of the rotor 15 and so on. The rotor 15 is composed of thepermanent magnet 14 and the valve shaft holder 12 fixed to the permanentmagnet 14 through the stop ring 13. Further, the permanent magnet 14(rotor 15) and a stator 20 compose a stepping motor.

The valve main body 5 is formed of metal such as brass and is providedwith the valve chamber 2 therein, and with the valve chamber 2communicates the first flow passage 3 and the second flow passage 4. Thevalve seat 6 is formed in a flow passage of the valve chamber 2 to thesecond flow passage 4 side. To the upper portion of the valve main body5 is fixed through welding the shield case 9 through a flange plate 22.In addition, on the right side face of the valve main body 5 stands astop ring 34 to fix the stator 20.

The valve body 7 is formed at the lower end portion of a valve shaft 24made of brass. The valve body 7 is formed to be acircular-truncated-cone shape in which an upper portion thereof is acolumn with larger diameter and a lower portion and an intermediateportion downwardly reduce their diameter. The shape of the valve body 7is one of the characteristics of the present invention, and this shapeprovides desired flow quantity characteristic.

In order to allow the valve body 7 to contact with and be separated fromthe valve seat 6, the male screw pipe 11, the valve shaft holder 12 andthe like are used. In the cylindrically formed male screw pipe 11, alower portion thereof is fixed to the valve main body 5 and the portionextends toward the rotor 15. On an intermediate outer surface of themale screw pipe 11 is threaded a male screw portion (driving screw) 25,which engages with a female screw portion 27 of the valve shaft holder12.

The valve shaft holder 12 positions outside of the male screw pipe 11and is formed to be a cylindrical shape opening downward. The femalescrew 27 is threaded on a lower inner face of the valve shaft holder 12.To an inner portion of the valve shaft holder 12 is fitted an upperportion with reduced diameter of the valve shaft 24, and those areconnected by a push nut 28.

The valve shaft 24 is provided with the valve body 7 at the lower endportion thereof, and is inserted in the valve shaft holder 12 so as tovertically be movable, and is always urged downward by a compressivecoil spring 29 that is mounted in the valve shaft holder 12 aftershrunk.

The shield case 9 is made of metal without magnetism such as stainlesssteel so as to be a cylindrical shape with a ceiling, and is fixedthrough welding or the like to the flange plate 22 at an upper portionof the valve main body 5. Inside of the shield case 9 is maintainedair-tightly.

The stator 20 is composed of a yoke 23 made of a magnetism material anda stator coil 10 wound on the yoke 23. The stator 20 is fitted outsideof the shield case 9. The stator 20 is fixed to the valve main body 5through the stop ring 34 by a locking member 20 a mounted on the bottomface.

A return spring 30 is composed of a compressive coil spring and ismounted to the outer circumference of the push nut 28 that is fixedthrough press to the upper end of the valve shaft 24. The return spring30 abuts the inner surface of the shield case 9 and urges it so as toreturn the engagement between the male screw portion 25 and the femalescrew portion 27 when the male screw portion 25 and the female screwportion 27 disengage with each other. The return spring 30 may beattached in a state that it is loosely fitted to and mounted on theouter circumference of the push nut 28 or resiliently be fitted to theouter circumference of the push nut 28.

The valve shaft holder 12 and the permanent magnet 14 are connected witheach other through the stop ring 13, and the stop ring 13 a metal(brass) ring that is inserted at the formation of the permanent magnet14. To the inner circumference of the stop ring 13 is fitted an upperprojecting potion of the valve shaft holder 12, and the outercircumference of the projection portion is fixed through caulking tointegrally connect the permanent magnet 14, the stop ring 13 and thevalve shaft holder 12.

To the male screw pipe 11 is fixed a lower stopper body (fixed stopper)33 that is a member composing a stopper mechanism. The lower stopperbody 33 is formed of resin and is ring-shaped, and a plate-like lowerstopper piece 33 a projects upward. On the other hand, to the valveshaft holder 12 is fixed an upper stopper body (movable stopper) 32 thatis another member composing the stopper mechanism, and the upper stopperbody 32 is also made of resin and is ring-shaped, and a plate-like upperstopper piece 32 a projects downward. The upper stopper piece 32 a ofthe upper stopper body 32 and the lower stopper piece 33 a of the lowerstopper body 33 are constructed such that they can abut each other.

Next, the motion of the motor-driven valve 1 with the above constructionwill be explained.

Feeding current to the stator coil 10 in a direction for magnetizationallows the rotor 15 including the permanent magnet 14 to rotate, whichcauses the valve shaft holder 12 to rotate in relation to the male screwpipe 11. Here, since the lower portion of the male screw pipe 11 isfixed to the valve main body 5, the screw-feeding mechanism by the malescrew portion 25 of the male screw pipe 11 and the female screw portion27 of the valve shaft holder 12 allows, for instance, the valve shaftholder 12 to move downward, which causes the valve body 7 to press thevalve seat 6 to close the valve opening.

The moment that the valve opening is closed, the upper stopper body 32does not abut the lower stopper body 33 yet, so that under the conditionthat the valve body 7 closes the valve opening, the valve shaft holder12 further drops while rotating. With this, the compression coil spring29 is compressed to absorb the force generated by the drop of the valveshaft holder 12. After that, when the rotor 15 further rotates to dropthe valve shaft holder 12, the upper stopper piece 32 a of the upperstopper body 32 abuts the lower stopper piece 33 a of the lower stopperbody 33 to forcibly stop the drop of the valve shaft holder 12 eventhrough current feeding to the stator coil 10 continues.

Next, feeding current to the stator coil 10 in another direction formagnetization allows the rotor 15 to rotate in an inverse direction tothe above-mentioned direction in relation to the male screw pipe 11fixed to the valve main body 5, and due to the screw-feeding mechanism,the valve shaft holder 12 moves upward, and the valve body 7 at thelower end of the valve shaft 24 is separated form the valve seat 6 toopen the valve opening. In the above motion, friction loss at the screwportion, or friction loss or torsion loss at the spring portion aregenerated.

Next, flow rate performance of the motor-driven valve 1 will beexplained mainly with reference to FIG. 2.

As stated above, the valve body 7 of the motor-driven valve 1 ischaracterized to have, in comparison to the valve body 77 of themotor-driven valve 70 shown in FIG. 6, lower height of the lowercircular-truncated-cone portion thereof and larger diameter in a whole,with this, the opening area of the valve seat 6 is also larger than thatof the valve seat 76 of the motor-driven valve 70.

With the above construction, 0 to 600 driving pulses are applied to thestator coil 10 of the stepping motor to control the valve opening, inthe range of the valve opening (approximately 50 to 400 pulses), whichis indicated by “C” in FIG. 2, flow rate of fluid changes almost inproportion to the valve opening. Next, between approximately 400 to 550pulses, the flow rate of fluid changes almost in proportion to the valveopening with larger inclination than that in the first valve openingrange, and between approximately 550 to 600 pulses, which is indicatedby “D” in FIG. 2, the flow rate of fluid becomes constant. With this, inthe second valve opening range D flow rate B becomes approximately sixtimes as much as controllable maximum flow rate A in the first valveopening range C.

Next, as an embodiment that the motor-driven valve 1 is used, a casethat the motor-driven valve 1 is used in place of the thermal expansionvalve 58 with a check valve in the cooling/heating system 51 shown inFIG. 5 will be explained mainly with reference to FIGS. 1 to 3.

As explained in “background art” column, in the cooling/heating system51 shown in FIG. 5, in cooling operation, refrigerant flows into thethermal expansion valve 58 with a check valve via the check valve 57 toperform insulation expansion, and then the refrigerant flows into theindoor heat exchanger 59. On the other hand, in heating operation, therefrigerant flows into the thermal expansion valve 58 with a check valvefrom the indoor heat exchanger 59, and the refrigerant is reduced inpressure, and then the refrigerant flows into the distributor 55. Here,it is necessary to control flow rate with the expansion valve portion ofthe thermal expansion valve 58 with a check valve in cooling, and toallow a large amount of refrigerant to flow in heating.

Then, in the flow illustrated in FIG. 5, in place of the thermalexpansion valve 58 with a check valve, the motor-driven valve 1 ismounted to allow refrigerant to flow from the first flow passage 3 tothe second flow passage 4 in cooling as shown in FIG. 3( a) as well asutilizing a minute clearance between the valve seat 6 and the lowerportion of the valve body 7, the motor-driven valve 1 controls the flowrate in the valve opening range C in FIG. 2. With this, it becomespossible to control flow rate of the refrigerant in cooling in the rangebetween 50 to 400 pulses.

On the other hand, in heating operation, as shown in FIG. 3( b), therefrigerant is to be flown from the second flow passage 4 to the firstflow passage 3, and the lower portion of the valve body 7 is caused tobe separated far from the valve seat 6 to allow the refrigerant to passin the second valve opening range D in FIG. 2. With this, a large amountof refrigerant can flow in heating in the range between 550 and 600pulses.

In addition, in the above embodiment, although it is constructed that inthe second valve opening range D in FIG. 2, the flow rate B that isapproximately six times as much as the controllable maximum flow rate Ain the first valve opening range C, the ration of the flow rate A to theflow rate B is appropriately changeable, and setting the ratio more orequal to four can constitute a motor-driven valve preferably used incooling/heating systems.

Here, in constituting the motor-driven valve described above, the rationof the valve opening area (the opening area between the valve seat 6 andthe valve body 7) of the valve seat 6 when whole pulses (600 pulses) areapplied to the valve opening area of the valve seat 6 when intermediatepulses (approximately 300 pulses) are applied can be four or more. Inaddition, the motor-driven valve can be constituted to have a valveopening area (opening area at an orifice portion) more or equal to threetimes as much as a theoretical valve opening area (opening area at anorifice portion) that is required to control flow rate of fluid in thefirst valve opening range C in FIG. 2.

Further, in case that the motor-driven valve 1 is used for thecooling/heating system 51, it is preferable that even through a largeamount of refrigerant passes the motor-driven valve 1, almost nopressure loss is generated. So, the ratio of the opening area (openingarea of the orifice portion) of the valve seat of the motor-driven valve1 to the minimum inner diameter of pipes used for the cooling/heatingsystem 51 is preferably be 0.2 or more.

In addition, the motor-driven valve 1 is provided with a larger openingarea of the valve seat 6 in comparison to conventional valves, so thatload that is calculated as a product of deferential pressure between twoflow passages 3 and 4 across the valve seat 6 and the opening area ofthe valve seat 6 becomes large. Therefore, in order to suppress theinfluence of the load low, the male screw portion 25 is formed to behave a small diameter, for instance, the ratio of nominal diameter ofthe male screw portion 25 to the opening are of the valve seat 6 ispreferably 1.3 or less. In addition, in order to reduce friction lossgenerated between the rotor 15 and the compression coil spring 29 in thevalve-opening motion of the rotor 15, the ratio of compression load tothe compression coil spring 29 in the open state of the valve to theproduct of deferential pressure between the two flow passages 3, 4across the valve seat 6 in the fully-closed state of the valve and theopening area of the valve seat 6 is preferably a half or less. In orderto maintain facial pressure to the screw portion appropriate and tosatisfy the above control performance against the increased load, theratio of the length of a complete screw portion of the male screwportion 25 to the nominal diameter of the male screw portion 25 ispreferably 0.75 or more. Further, as shown in FIG. 4, it is preferablethat an angle αbetween the side face 7 a of the lowercircular-truncated-cone portion of the valve body 7 and the axis of thevalve body 7 is 15 degree or less, and the ratio of the length of theside face 7 a in a direction of the axis to moving amount of the valvebody 7 over whole pulse width is 0.7 or less. In addition, the diameterof the opening of the valve seat 6 is preferably 3 mm or more.

Meanwhile, in the above embodiment, although the explanation was made incase that the motor-driven valve 1 is used in place of the thermalexpansion valve 58 with a check valve of the cooling/heating system 51shown in FIG. 5, the valve 1 may be used in place of the thermalexpansion valve 56 or the check valve 57. Further, besides thecooling/heating system 51, the motor-driven valve 1 is applicable toother systems utilizing the flow rate performance as shown in FIG. 2.

1. A motor-driven valve having a valve body linearly moving by rotationof a rotor of an electric motor and controlling a valve opening betweenthe valve body and a valve seat, said motor-driven valve characterizedin that: in a first valve opening range, said valve opening and a flowrate of fluid have a predetermined correlation, and in a second valveopening range, a flow rate more than four times as much as acontrollable maximum flow rate in the first valve opening range can passthrough the valve.
 2. The motor-driven valve as claimed in claim 1,wherein driving pulses are fed to a driving coil of the electric motorto control the valve opening, and the ratio of an opening area of thevalve seat when whole pulses are applied to the area when intermediatepulses are applied is four or more.
 3. The motor-driven valve as claimedin claim 1, wherein driving pulses are fed to a driving coil of theelectric motor to control the valve opening; an opening area of thevalve seat is three times or more than a theoretical opening range ofthe valve seat that is required to control flow rate of the fluid in thefirst valve opening area; the fluid flow rate in the first valve openingrange is controlled with driving pulses of which width is in a rangebetween more or equal to a quarter and less or equal to two-thirds ofwhole pulses; and the valve opening is controlled to be maximum withdriving pulses when whole pulses are applied.
 4. The motor-driven valveas claimed in claim 3, wherein at the maximum valve opening fluid flowsin an opposite direction to that of fluid flowing in the first valveopening range.
 5. The motor-driven valve as claimed in claim 2, whereinthe ratio of the opening are of the valve seat of the motor-driven valveto a minimum inner cross-sectional area of pipes in a system with themotor-driven valve is 0.2 or more.
 6. The motor-driven valve as claimedin one of claims claim 1, wherein further comprising a driving screw forconverting the rotational motion of the rotor to the linear motion ofthe valve body, the ratio of a nominal diameter of the driving screw toa diameter of the valve seat opening being 1.3 or less.
 7. Themotor-driven valve as claimed in claim 1, wherein a spring is disposedbetween the valve body and the rotor, for urging the valve body to thevalve seat side, and the ratio of compression load to the spring in afully-closed state of the valve to the product of differential pressurebetween two flow passages across the valve seat in the fully-closedstate of the valve and the opening area of the valve seat is a half orless.
 8. The motor-driven valve as claimed claim 6, wherein the ratio ofa length of a complete screw portion of the driving screw to the nominaldiameter of the driving screw is 0.75 or more.
 9. The motor-driven valveas claimed in claim 1, wherein a tip portion of the valve body is formedto be a circular-truncated-cone shape with reduced diameter toward thetip side; fluid flow rate is controlled by a portion between a side faceof the circular-truncated-cone portion and an inner circumferential faceof the valve seat opening; an angle between the side face of thecircular-truncated-cone portion and an axis of the valve body is 15degree or less; and the ratio of a length of the side face in adirection of the axis to moving amount of the valve body over wholepulse width is 0.7 or less.
 10. The motor-driven valve as claimed inclaim 1, wherein the diameter of said valve seat opening is more orequal to 3 mm.
 11. A cooling/heating system with a motor-driven valvehaving a valve body linearly moving by rotation of a rotor andcontrolling a valve opening between the valve body and a valve seat,said motor-driven valve characterized in that: in a first valve openingrange, a flow rate in cooling operation is controlled, and in a secondvalve opening range, in heating operation, refrigerant more than fourtimes as much as a controllable maximum flow rate of refrigerant in thecooling operation can pass through the valve.
 12. The motor-driven valveas claimed in claim 3, wherein the ratio of the opening are of the valveseat of the motor-driven valve to a minimum inner cross-sectional areaof pipes in a system with the motor-driven valve is 0.2 or more.
 13. Themotor-driven valve as claimed in claim 4, wherein the ratio of theopening are of the valve seat of the motor-driven valve to a minimuminner cross-sectional area of pipes in a system with the motor-drivenvalve is 0.2 or more.
 14. The motor-driven valve as claimed in claim 2,further comprising a driving screw for converting the rotational motionof the rotor to the linear motion of the valve body, the ratio of anominal diameter of the driving screw to a diameter of the valve seatopening being 1.3 or less.
 15. The motor-driven valve as claimed inclaim 3, further comprising a driving screw for converting therotational motion of the rotor to the linear motion of the valve body,the ratio of a nominal diameter of the driving screw to a diameter ofthe valve seat opening being 1.3 or less.
 16. The motor-driven valve asclaimed in claim 4, further comprising a driving screw for convertingthe rotational motion of the rotor to the linear motion of the valvebody, the ratio of a nominal diameter of the driving screw to a diameterof the valve seat opening being 1.3 or less.
 17. The motor-driven valveas claimed in claim 5, further comprising a driving screw for convertingthe rotational motion of the rotor to the linear motion of the valvebody, the ratio of a nominal diameter of the driving screw to a diameterof the valve seat opening being 1.3 or less.
 18. The motor-driven valveas claimed in claim 6, wherein a spring is disposed between the valvebody and the rotor, for urging the valve body to the valve seat side,and the ratio of compression load to the spring in a fully-closed stateof the valve to the product of differential pressure between two flowpassages across the valve seat in the fully-closed state of the valveand the opening area of the valve seat is a half or less.
 19. Themotor-driven valve as claimed in claim 18, wherein the ratio of a lengthof a complete screw portion of the driving screw to the nominal diameterof the driving screw is 0.75 or more.